Download KA3842/43/44/45

Inv № 59
Current Mode PWM Controller
KA3842/43/44/45
July 1995 - revised July 2002
DESCRIPTION
KA3842/43/44/45 are fixed frequency current mode PWM
controller. They are specially designed for OFF−Line and DC to DC converter applications
with a minimal external components. Internally implemented circuits include a trimmed
oscillator for precise duty cycle control, a temperature compensated reference, high gain
error amplifier, current sensing comparator, and a high current totempole output ideally
suited for driving a power MOSFET. Protection circuitry includes built undervoltage lockout
and current limiting.
The UC3842A(AM) and UC3844A(AM) have UVLO thresholds of 16 V (on) and 10 V (off).
The corresponding thresholds for the UC3843A(AM)/45A(AM) are 8.4V (on) and
7.6V
(off). The UC3842A(AM) and UC3843A(AM) can operate within 100% duty cycle. The
UC3844A(AM) and UC3845A(AM) can operate within 50% duty cycle.
The UC384XA(AM) has Start-Up Current 0.17mA (typ).
FEATURES
•
•
•
•
Low Start-Up and Operating Current
High Current Totem Pole Output
Undervoltage Lockout With Hysteresis
Operating Frequency Up To 300KHz
(384XA)
500KHz
(384XAM)
BLOCK DIAGRAM
(toggle flip flop used only in UC3844, UC3845)
Absolute Maximum Ratings
Characteristic
Supply Voltage (low impedance
source)
Output Current
Symbol
VCC
Value
30
Unit
V
IO
±1
A
Input Voltage (Analog Inputs pins 2,3)
VI
Error Amp Output Sink Current
Power Dissipation (TA=250C)
Storage Temperature Range
Lead Temperature (soldering 5 sec.)
ISINK (E.A)
PO
Tstg
TL
−0.3 to 5.5
10
1
-65 to150
260
mA
W
oC
oC
1
V
PIN
CONNECTION
(TOP VIEW)
Inv № 59
Current Mode PWM Controller
KA3842/43/44/45
July 1995 - revised July 2002
Electrical characteristics (*VCC=15V, RT=10kΩ, CT=3.3nF, TA=00C to +700C, unless otherwise
specified)
Characteristics
Symbol
Test Condition
Min
Typ
Max
Reference Section
Reference Output Voltage
5.0
5.1
V
Line Regulation
∆VREF
12V ≤ VCC ≤ 25 V
6.0
20
mV
Load Regulation
∆VREF
ISC
1 mA ≤ IREF ≤ 20mA
6.0
25
-100
-180
50
52
0.05
57
57
1.0
Short Circuit Output Current
VREF
TJ = 25°C, IREF = 1 mA
4.9
Unit
TA = 25°C
mA
Oscillator Section
Oscillation Frequency
f
TJ = 25°C
384XA
384XAM
Frequency Change with
Voltage
Oscillator Amplitude
Error Amplifier Section
Input Bias Current
∆f/∆VCC
Input Voltage
Open Loop Voltage Gain
VI(E.A)
AVOL
Vpin1 = 2.5V
Power Supply Rejection Ratio
PSRR
12V ≤ VCC ≤ 25 V
Vpin2 = 2.7V, Vpin1 = 1.1V
Vpin2 = 2.3V, Vpin1 = 5V
Output Sink Current
Output Source Current
High Output Voltage
Low Output Voltage
Current Sense Section
Gain
Maximum Input Signal
Supply Voltage Rejection
V(OSC)
IBIAS
ISINK
ISOURCE
VOH
VOL
GV
VI(MAX)
SVR
Input Bias Current
IBIAS
Output Section
Low Output Voltage
VOL
High Output Voltage
VOH
Rise Time
tR
Fall Time
tF
Undervoltage Lockout Section
Start Theshold
VTH(ST)
Min. Operating Voltage
(After Turn On)
PWM Section
Max. Duty Cycle
Min. Duty Cycle
Total Standby Current
VOPR(min)
D(MAX)
47
47
12V ≤ VCC ≤ 25 V
(peak to peak)
1.6
VFB=3V
2V ≤ V0 ≤ 4V
Vpin2 = 2.3V, RL = 15KΩ to GND
KHz
%
V
-0.1
-2
2.42
65
2.5
90
2.58
60
70
2
-0.5
5.0
7
-1.0
6.0
µA
V
dB
mA
mA
V
0.8
1.1
3.0
1.0
70
3.15
1.1
V/V
V
dB
-3.0
-10
µA
0.4
2.2
TJ = 25°C, CL = 1nF (Note 3)
0.08
1.4
13.5
13.0
45
150
TJ = 25°C, CL = 1nF (Note 3)
35
150
Vpin2 = 2.7V, RL = 15KΩ to PIN 8
(Note 1 & 2)
V pin1 = 5V (Note1)
2.85
0.9
12V ≤ VCC ≤ 25 V (Note 1)
Vpin3 = 3V
ISINK
ISINK
ISINK
ISINK
=
=
=
=
20 mA
200 mA
20 mA
200 mA
13
12
UC3842A(AM)/44A(AM)
UC3843A(AM)/45A(AM)
UC3842A(AM)/44A(AM)
UC3843A(AM)/45A(AM)
14.5
7.8
8.5
7.0
16.0
8.4
10
7.6
17.5
9.0
11.5
8.2
UC3842A(AM)/43A(AM)
UC3844A(AM)/45A(AM)
95
47
97
48
100
50
0
0.17
0.3
13
38
17
D(MAX)
IST
UC384XA(AM)
Start−Up Current
Operating Supply Current
ICC (OPR)
Vpin3 = Vpin2 = 0V
Zener Voltage
VZ
ICC=25 mA
30
* Adjust VCC above the start threshold before setting it to 15V.
Note 1: Parameter measured at trip point of latch with Vpin2=0.
Note 2: Gain defined as A=∆Vpin1/∆Vpin3 ; 0 ≤ Vpin3 ≤ 0.8V.
Note 3: These parameters, although guaranteed, are not 100% tested in production.
2
V
nS
V
V
%
mA
V
Inv № 59
Current Mode PWM Controller
KA3842/43/44/45
July 1995 - revised July 2002
PIN FUNCTION
N
1
2
FUNCTION
COMP
VFB
3
ISENSE
4
RT/CT
5
6
GROUND
OUTPUT
7
8
VCC
Vref
DESCRIPTION
This pin is the Error Amplifier output and is made for loop compensation.
This is the inverting input of the Error Amplifier. It is normally connected to the
switching power supply output through a resistor divider.
A voltage proportional to inductor current is connected to this input. The PWM
uses this information to terminate the output switch conduction.
The oscillator frequency and maximum Output duty cycle are programmed by
connecting resistor RT to Vref and capacitor CT to ground.
This pin is the combined control circuitry and power ground.
This output directly drives the gate of a power MOSFET. Peak currents up to 1A
are sourced and sink by this pin.
This pin is the positive supply of the integrated circuit.
This is the reference output. It provides charging current for capacitor CT through
resistor RT .
APPLICATION INFORMATION
Figure 1. Error Amp Configuration
Figure 2. Undervoltage Lockout
3
Inv № 59
Current Mode PWM Controller
KA3842/43/44/45
July 1995 - revised July 2002
Figure 3. Current Sense Circuit
Figure 4. Slope Compensation Techniques
4
Inv № 59
Current Mode PWM Controller
KA3842/43/44/45
July 1995 - revised July 2002
SCR must be selected for a holding current of less than 0.5mA.
The simple two transistor circuit can be used in place of the SCR as shown.
Figure 5. Latched Shutdown
Figure 6. Error Amplifier Compensation
5
Inv № 59
Current Mode PWM Controller
KA3842/43/44/45
July 1995 - revised July 2002
Figure 7. External Clock Synchronization
Figure 8. Soft-Start Circuit
6
Inv № 59
Current Mode PWM Controller
KA3842/43/44/45
July 1995 - revised July 2002
TYPICAL PERFORMANCE CHARACTERISTICS
Figure 1. Timing Resistor vs. Oscillator Frequency
Figure 2. Output Dead-Time vs. Oscillator Frequency
Figure 3. Maximum Output Duty Cycle vs.
Timing Resistor (UC3842/43)
Figure 4. Error Amp Open-Loop Gain vs.
Frequency
Figure 5. Current Sense Input Threshold vs.
Error Amp Output Voltage
Figure 6. Reference Short Circuit Current vs.
Temperature
7
Inv № 59
Current Mode PWM Controller
KA3842/43/44/45
July 1995 - revised July 2002
Figure 7. Output Saturation Voltage vs. Load Current
TA = 25°C
Figure 8. Supply Current vs. Supply Voltage
Figure 9. Oscillator and Output Waveforms
8
Inv № 59
Current Mode PWM Controller
KA3842/43/44/45
July 1995 - revised July 2002
PAD LOCATION
Chip size: 2.38 x 1.63 mm
Pad N
Pad Name
1
2
3
4
5
6
7
8
9
10
COMP
VFB
ISENSE
RT/CT
POWER GND
GND
OUT
POWER VCC
VCC
VREF
Coordinates µm
X
Y
90
110
1050
110
1310
110
2000
150
1700
1280
1680
1450
1310
1410
990
1410
815
1410
460
1390
9